It has been recognized that a serious problem with wood burning furnaces is the effects of incomplete combustion. Incomplete combustion results in the emission of pollutants, the deposition of the products of the incomplete combustion on the various elements within the furnace and in failure to achieve peak efficiency. A number of proposals have been made to reduce the level of uncombusted materials given off by solid fuel burning devices including the use of secondary combustion chambers.
It has been discovered that by passing the flue gases containing the products of incomplete combustion through a tunnel the walls of which have been rendered incandescent by the passage of hot flue gases therethrough, a substantial increase in the pyrolysis of the flue gases occurs, thereby resulting in reduction of the level of uncombusted materials in the gases.
The device contemplated for carrying out this method utilized a straight tunnel having relatively thick walls composed of refractory material and connecting a combustion chamber to a heat exchanger base portion. Because the tunnel could not be less than a certain minimum length in order to provide adequate dwell time to complete pyrolysis, there resulted a furnace which was relatively large because of the necessary separation of these two chambers to accommodate the connecting tunnel. Such a device was also heavy due to the relatively thick walls of the tunnel.